This invention relates to apparatus for mounting a sidecar to a motorcycle having a trapezoid frame section.
Present-day motorcycles are provided with frames including a vertically disposed, trapezoid-shaped section 10 of the type shown in FIG. 1 of the drawings. The trapezoid frame section is defined by a plurality of interconnected struts including an elongate upper strut 12 extending from the rear 14 to the front 16 of the motorcycle, a lower strut 18, a rear diagonal strut 20 and a front diagonal strut 22. Lower strut 18 is beneath and substantially parallel to upper strut 12. Rear diagonal strut 20 extends between the respective back ends of upper strut 12 and lower strut 18. Front diagonal strut 22 extends between the respective front ends of upper strut 12 and lower strut 18.
The junctures of the various struts define a first vertex 24 of the trapezoid, a second vertex 26 and a third vertex 28. The juncture of the rear diagonal strut 20 and the upper strut 12 defines first vertex 24 adjacent a seat cushion 27. Rear diagonal strut 20 and front diagonal strut 22 respectively define, with lower strut 18, second and third vertices 26 and 28. Vertices 26 and 28 are both substantially below and in front of first vertex 24 and are aligned parallel with upper strut 12. An intermediate diagonal strut 30 extends from adjacent the second vertex 26 to a point on the upper strut 12 in front of second vertex 26.
The remaining parts of the motorcycle are mounted to frame section 10. A rear wheel 32 is secured to the rear diagonal strut 20 by means of a swing arm suspension system including a pivotally mounted swing arm 34 and a dashpot shock absorber 36. A steering column 38 is mounted within a bearing housing 39 which is secured to an extension of front diagonal strut 22. A front wheel assembly 40 is rotatably mounted at the free end of a fork assembly 42 which is carried by steering column 38. An engine 44 is mounted to the frame between intermediate diagonal strut 30 and front diagonal strut 22. Other parts of the motorcycle, not shown, such as a gas tank, fenders, etc., are also carried by the frame.
In addition to engine 44, the gas tank and other parts of the motorcycle, the frame must carry the load of the motorcycle rider and sometimes a passenger and luggage. Known arrangements for mounting a sidecar to a motorcycle attach the sidecar to the motorcycle at various locations on the frame. A sidecar, when mounted to the frame, further increases the load forces that are applied thereto.
The points on the trapezoid frame section at which the sidecar is connected is a matter of great importance. The foremost consideration in selecting the connection points is that the additional sidecar load forces applied to the frame may be sufficiently great to misalign and bend the frame elements depending upon the locations on the frame at which they are applied. A further consideration in locating the connection points of a mounting apparatus is the spacing between connection points. The greater the distance between connection points, the greater the mechanical advantage of the connectors in resisting forces tending to pivot apart the sidecar and the motorcycle. Yet another consideration in selecting a mounting apparatus arrangement of connection points on the trapezoid frame is the extent such locations facilitate attachment of mounting brackets or the like to the frame members. Likewise, the connection points should enable the use of mounting brackets which do not require permanent alteration or permanent attachment to the frame, or which weaken the frame. The connectors should not interfere with the comfortable seating and leg positioning of the rider or passenger. Preferably, to minimize costs and to facilitate sidecar attachment to, and detachment from, the motorcycle, the number of connection points should be minimized. Moreover, the location of the connection points should be selected so as not to interfere with the provision of a wheel suspension system for the motorcycle.
Known apparatus for mounting a sidecar to a trapezoid-shaped frame section lack many of the advantageous characteristics noted above. For example, in one known mounting apparatus, connections to the rear and front diagonal struts intermediate their ends have resulted in these frame members being bent by sidecar forces.